The present invention relates to a semiconductor circuit for providing protection against electrical overstress (EOS) and a design structure for the same.
An electrical overstress (EOS) event is a temporary electrical discharge in an electronic circuit that is caused by an unusual spike in the voltage applied to the electronic circuit. An EOS event causes damages at the electronic component or board level, triggering a system failure or a component failure. An EOS event usually lasts from a few microseconds to a few seconds.
When the EOS damages are at the electronic device level, such damages are typically invisible. EOS damages may be manifested, for example, as a damages metal line that is electrically open or a structure melted by high power consumption. Electrostatic discharge (ESD) events are a subset of EOS events. The ESD events have a duration less than 1 microsecond, and typically have a duration in a picoseconds range or in a nanoseconds range. Powered EOS events, i.e., EOS events in which a power source provides the source of the electrical discharge, may last over 1 millisecond, and may last up to a few seconds in duration.
An EOS event may be induced by many different causes. For example, when a plug or an electronic component is plugged into an operational electronic circuit, an EOS event may be caused by such a “hot plugging.” Power supplies can cause an EOS event if they fail to regulate the power supply voltage and amperage properly and cause power spikes. Improper operating practice of electronic equipments may also cause an EOS event. Such improper operating practice includes incorrect positioning of electronic components, incomplete seating of connections, and improper power up or power down sequences. Also, ground bounce may case an EOS event. Ground bounce may be caused by turning on of a large current-consuming device, such as an electrical motor or a large electronic component. The ground bounce induces a fast current switching that results in high voltage due to insufficient grounding points. In addition, high potential device testing may cause an EOS through a voltage surge or power spike generation.
While an electrostatic discharge (ESD) protection circuit is typically employed in semiconductor devices to provide protection against ESD events that generate a voltage spike having a duration up to a microsecond or so, such an ESD protection circuit does not provide protection from a voltage spike having a duration greater than 1 microsecond. However, as electronic devices scale down for higher density and performance, the probability of EOS events having a duration greater than 1 millisecond increases.
In view of the above, there exists a need for an electrical overstress (EOS) protection circuit that provides protection against a power spike having a duration grater than 1 millisecond and up to a few seconds, and a design structure for the same.
Further, there exists a need for an EOS protection circuit that provides protection against such a power spike as well as providing protection against typical ESD events having a duration less than 1 millisecond, and a design structure for the same.